Zirconium alloys



ZIRCONIUM ALLOYS Thomas Raine, Bramhall, and James Alan Robinson,

Bolton, England, assignors to Metropolitan-Vickers Electrical Company Limited, London, England, a

British company No Drawing. Appllcation July 7, 195a Serial No. 746,605

Claims priority, application Great Britain July 26, 1957 5 Claims. on. 75-111 This, invention relates ,to alloys suitable, inter alia, for use at high temperatures in an atmosphere of carbon dioxide.

Conditions arise, in the core of graphite moderated nuclear reactors in which carbon dioxide is used for cooling and heat extraction, where metallic parts are brought, under operating conditions, into contact with carbon dioxide at a high temperature. Normal structural materials, such as steel cannot be employed in these conditions because of their high neutron absorption.

Consideration has been given to the use of alloys of zirconium in such reactors. A known alloy of zirconium, Zircaloy-2, which contains l.3-l.6% tin, 0.070.2% iron, 0.050.15% chromium and 0.03-0.08% nickel, possesses good strength, and has a low neutron cross-section. But in the temperature range above 400 C. its resistance to corrosion by carbon dioxide is inadequate.

It has now been discovered, however, that when used in contact with carbon dioxide at temperatures up to 600 C. an alloy of zirconium with copper and molybdenum or chromium is both resistant to corrosion and has improved resistance to creep.

Zirconium alloys in accordance with the present invention contain 0.51.5% by weight of copper, and from 0.25-1.5% by weight of molybdenum or chromium, the

remainder consisting wholly of zirconium, except for unavoidable impurities which are normally found in the commercial material, known as sponge zirconium, which is preferably used as the source of zirconium in the alloy.

Two alloys which constitute preferred embodiments of the invention are:

Example 1Cu, 0.5%; M0, 0.5%; remainder Zr Example 2Cu, 1.0%; M0, 1.5%; remainder Zr The following mechanical properties of the improved alloys in comparison with zirconium and Zircaloy-2 are as follows:

Hardness tests at room temperature V.P.N. represents Vickers Pyramid Number.

These tests showed the improved hardness of the alloys of the invention over zirconium and Zircaloy-Z.

Hardness tests at a temperature of 500 C. with creasing times of load application and compared with 1 Zircaloy-Z showed the following results:

V.P.N.

Alloy 3 30 300 3,000 secs. secs. secs. secs.

Zircaloy2. 60 52 38 30 Example (2)- 66 61 59 55 The specimens of both alloys were annealed at 820 C. in vacuo prior to testing.

Tests made at 475 C. indicated that Example 1 alloy was slightlyhardcr for the longest-period of load application, and slightly less hard for the shorter periods of 5 load application than Zircalo'y-Z."

The tensile strength of the improved zirconium alloys of the invention at roomtemperature, after annealing at 820 C. showed increases over that of Zircaloy-Z. Specimens of Example 1 alloy were about 20% better, and of Example 2 alloy about better than those of Zircaloy-2," the percentage elongation of specimens of Example l was about the same as that of Zircaloy-Z, while that of Example 2 was about two-thirds that of Zircaloy 2. This improvement was increased when the specimens were tested at 375 C.

Tensile creep tests at 6,000 psi. the specimens being tested in an atmosphere of argon, showed the following results:

Temp. Time in hours to reach a of strain of- Alloy Condition Tag,

Zlrcaloy-2 Arsiggglgd at 450 800 1, 500 5, 300 6, 600 Do do 476 300 600 1, 040 2, 240 D0 n 500 275 480 810 Example (1) Aggg tld at 450 860 1, 960 5, 500 Example (2) do 475 500 900 1, 700 3,800

The increase in creep resistance of the improved alloys over that of Zircaloy-2 was greater the higher the percentage strain.

The reaction to corrosion by CO, is illustrated by results given below of tests at 700 C. and one atmosphere gas pressure.

Time to reach Post transition Alloy 50 mg./cm.1 Corrosion rate,

hours Zirconium--. 1, 200 50. 1x10- Z1rcaloy-2. 870x10 Example (1) 5, 000 11. 4x10- Example (2) 5, 000 9. 4X10- cm." relative to a cross-section in barns/atom of 0.20, then the corresponding eross-seetions of Example 1 and Example 2 are 0.012386 cm.- and 0.015126 cm.- respectively.

The high temperature mechanical properties of zirconium-copper-molybdenum and zirconium-copper-chromium alloys mentioned above can be further improved by heat treatment, which consists of heating the alloy to a temperature of 850 C. to 950" C. and maintaining the temperature for a specified time before quenching to reduce the temperature of the alloy rapidly. This treatment may then be followed by a tempering treatment which consists of reheating the alloy for a specified time at a temperature below 850 C.

Arising from the ability of zirconium to oxidise and to absorb atmospheric and other impurities readily at elevated temperatures, the constituents of the alloy should be melted in a vacuum arc furnace. Apart from this restriction the alloys of the invention can be readily fabricated by conventional methods.

Impurities in the base zirconium sponge should be kept to a minimum. The most deleterious impurities from the corrosion resistance point of view are. aluminium, silicon, hydrogen, xygenr i s n. a it ni m. l minium should be kept below 150 parts per million, whilst nitrogen and'titanium are not so injurious, and in the latter case, and titanium content may be as high as 1,000

. 4 parts per million without appreciably affecting the corrosion resistance of the alloys.

What we claim is:

1. An alloy consisting of 0.5 to 1.5% by weight of copper, 0.25 to 1.5% by weight of a metal selected from the group consisting of chromium and molybdenum, and the remainder zirconium except for unavoidable impurities.

2. An alloy as claimed in claim 1 and intended to be employed at a high temperature in contact with carbon dioxide, in which impurities, such as aluminium and titanium are restricted to the order of 100 parts per million, by weight.

3. An alloy as claimed in claim 1, in which the source of zirconium used in making'the alloy is that commercially known as sponge zirconium.

4. An alloy consisting of 0.5% by weight, of copper, 0.5% by weight, of molybdenum and the remainder zirconium except for unavoidable impurities.

5. An alloy of 1.0% by weight copper, 1.5% by weight of molybdenum, and the remainder zirconium except for unavoidable impurities.

References Cited in the file 015 this patent UNITED STATES PATENTS 2,705,674 Chubb Apr. 5, 1955 

1. AN ALLOY CONSISTING OF 0.5 TO 1.5% BY WEIGHT OF COPPER, 0.25 TO 1.5% BY WEIGHT OF A MERAL SELECTED FROM THE GROUP CONSISTING OF CHROMIUM AND MOLYBDENUM, AND THE REMAINDER ZIRCONIUM EXCEPT FOR UNAVOIDABLE IMPURITIES. 